Correlated normative and experimental studies are planned to test the hypothesis that the temporal order of neurogenesis is the initial contributing factor in the establishment of neural connections within the olfactory and limbic systems. Project I is to complete normative dating of the time of origin of neurons in the olfactory system using the new, improved progressively delayed comprehensive labeling procedure of 3H-thymidine radiography which allows one to calculate the proportion of neurons arising over single days during development. Morphogenetic studies will be done in conjunction with project I, including a volumetric analysis of morphogenesis in the olfactory bulb, a quantitative analysis of neuroepithelial zones in the basal telencephalon, and a study to follow the migration of olfactory bulb output neurons from their neuroepithelial sources to their final locations. Project II is to examine experimentally the correlations between time of origin of neurons and their patterns of anatomical connections. A) The development of the entorhinal projection to the dentate molecular layer will be traced using iontophoretic injections of conjugated wheat-germ agglutinin and horseradish peroxidase (WGA-HRP) during late embryonic and early postnatal life. B) 3H-thymidine radiography and WGA-HRP iontophoretic injections will be combined to determine the correlation between time of mitral cell origin and their sites of axonal termination in the cortical nucleus of the amygdala. This research will have importance for two reasons. On the one hand, it will allow the testing of a viable hypothesis about one of the mechanisms involved in the regulation of embryonic development of the nervous system. On the other hand, it will fill a gap in our knowledge about the development of the olfactory and limbic systems.